In your WordPress dashboard, go to Appearance > Themes. At the top, click “Add New,” and then click “Upload Theme” on the next page.
Click Choose File. Locate the mia-theme.zip file that came with your theme and upload it. (Note: your theme may have a version number behind it, such as mia-theme.1.9.zip).
Click Install Now and wait for the theme to install. Activate the theme.
If you received a "missing style.css stylesheet" error, you've uploaded the incorrect file.
Click here for further details.